As cars become a common transportation vehicle and portable electronic devices, such as, smart phone and tablet PC, become a mainstream communication and entertainment gadget, the use of portable devices in cars creates a demand in auxiliary apparatus for using portable devices in cars. While the driver using portable device may pose potential hazard, the passenger using portable device inside vehicle is a good way to stay entertained.
To provide good riding environment for backseat passengers, some manufacturers developed auxiliary apparatus applicable to seat backrest inside a vehicle. These known auxiliary apparatuses are often fastened to the posts supporting the headrest on the back of the seat backrest of the front seat for holding portable electronic device, such as, tablet, for viewing by the back seat passengers. However, such auxiliary apparatus is not convenient for two back seat passengers to view the same device, in particular, for the passenger not directly behind the front seat equipped with the auxiliary apparatus. It is desirable to devise a positioning apparatus able to provide different modes for a single passenger or for two or more passengers sharing the electronic device.